1. Field of the Invention
The present invention relates to a recording apparatus such as a thermal printer, an electronic typewriter, a facsimile system, or an ink-jet printer and, more particularly, to a recording apparatus for recording an image such as characters and figures on a recording sheet by driving a recording head with heating elements.
2. Description of the Prior Art
A conventional recording apparatus of this type has a density volume control for controlling the recording density at an optimal or desired level. A voltage applied to the recording head is varied in accordance with different volume control positions, and the energization time is fixed.
The energization time of the recording head, however, is determined in accordance with an optimal density range. When the density volume control is adjusted to obtain a density falling outside this range, a high-quality image at the desired high or low density is often unattainable. Furthermore, thermal characteristics of the recording head in the conventional recording apparatus inevitably influence recording quality, and the recording density varies in accordance with ambient temperature, as is well known to those skilled in the art. In the conventional apparatus, a temperature sensor such as a thermistor is used to determine a time constant of a monostable multivibrator. The recording head is driven for an output time of the multivibrator operated corresponding to changes in ambient temperature.
The ambient temperature-recording density characteristics, however, do not coincide with the detection characteristics of the temperature sensor over the entire range of operation. Although a density difference caused by an ambient temperature can be compensated for to some extent, correction cannot be properly performed in a given temperature range. As a result, a uniform density cannot be obtained throughout the entire temperature range.